Speedo now reading in reverse

[AB]

I've read through a few speedo issues and solutions other members have had on here but this one seems a little different.

After heavy corrugations at our Easter break I noticed the speedo was jolting around within 10km's of actual speed whilst we were away.

On the way home on the freeway doing 110km's the speedo fell to the other side of the gauge (Reading 200km's) and stayed there.

Now it sits on that side at idle but when you drive the car it starts to read backwards and will read 140km's at 60km travel, etc.

It's almost like It's reading in reverse now???

Does anyone have any suggestions or things I can look at to isolate the problem or should I just get a whole new cluster or?

[MudRunnerTD]

Yes very strange indeed. Rodney might shed some light hopefully.

[the evil twin]

Just drive around backwards... problem solved.

Probably cause a few bowel movements on the Motorway but thats life

If the Odometer is going backwards as well I'd leave it as it is for 100,000 or so

[AB]

Just drive around backwards... problem solved.

Probably cause a few bowel movements on the Motorway but thats life

If the Odometer is going backwards as well I'd leave it as it is for 100,000 or so

I didn't actually check that...lol

[TPC]

Mudnut has been setting himself up to test and repair GQ instrument clusters, wonder if he would have any idea.
Does everything else work ok?

[mudnut]

Bear with me as I am still setting things up. I have just pulled the tb42e unit apart to sus out what may be going on with yours, Andy. It is just a moving coil meter, with two field windings instead of one.(one powered from ignition and one powered by the speedo sender which is cleaned up by the speedo electronics) I think that the two windings provide for stability and give a more accurate reading. At this stage I can only guess that there is a fault in the speedo electronics as the speed sensor sends an AC signal. There may be a blown diode which is letting the AC signal through. The heavy vibrations may have interfered with the pointer spring too. I would need to have a look at your speedo, too test it properly.

[mudnut]

Yours is a TB42 E isn't it Andy? With ignition off. If you take off the dash surround and undo the four cluster screws then lift out the cluster and tilt it to see the back. You should be able to see the speedo signal and power inputs, which are four silver phillip drive cheese head screws. Looking from the above, top one is marked 2P, the bottom is IGN. The side ones have a bit of Japenese followed by - and +. These are the speedo signal inputs. To get a good measurement, I made two 50cm long test leads, by stripping a half centimetre of the insulation from each end. Loosen the -ve and +ve. Slip one lead under the -ve and tighten the screw, making sure that no strands of copper are loose and able to contact any other part of the circuit. Do the same for the+ ve. Re position the cluster and do up the four anchor screws. I taped the other ends of the test leads to the probes of a digital multimeter and set the dial to AC volts. Get an assistant to drive. See that you get a small voltage which should rise to approx 5 volts as the speed increases to 60kph. When you have finished, remove the leads and re tighten the screws, firmly, but do not over torque them. Sorry, pictures won't load at the moment.

Edit, changed the signal output to approximately 5 volts

[MudRunnerTD]

Yours is a TB42 E isn't it Andy? With ignition off. If you take off the dash surround and undo the four cluster screws then lift out the cluster and tilt it to see the back. You should be able to see the speedo signal and power inputs, which are four silver phillip drive cheese head screws. Looking from the above, top one is marked 2P, the bottom is IGN. The side ones have a bit of Japenese followed by - and +. These are the speedo signal inputs. To get a good measurement, I made two 50cm long test leads, by stripping a half centimetre of the insulation from each end. Loosen the -ve and +ve. Slip one lead under the -ve and tighten the screw, making sure that no strands of copper are loose and able to contact any other part of the circuit. Do the same for the+ ve. Re position the cluster and do up the four anchor screws. I taped the other ends of the test leads to the probes of a digital multimeter and set the dial to AC volts. Get an assistant to drive. See that you get a small voltage which should rise to approx 2 volts as the speed increases. When you have finished, remove the leads and re tighten the screws, firmly, but do not over torque them. Sorry, pictures won't load at the moment.

ABs is a TD42 Craig.

[AB]

Yours is a TB42 E isn't it Andy? With ignition off. If you take off the dash surround and undo the four cluster screws then lift out the cluster and tilt it to see the back. You should be able to see the speedo signal and power inputs, which are four silver phillip drive cheese head screws. Looking from the above, top one is marked 2P, the bottom is IGN. The side ones have a bit of Japenese followed by - and +. These are the speedo signal inputs. To get a good measurement, I made two 50cm long test leads, by stripping a half centimetre of the insulation from each end. Loosen the -ve and +ve. Slip one lead under the -ve and tighten the screw, making sure that no strands of copper are loose and able to contact any other part of the circuit. Do the same for the+ ve. Re position the cluster and do up the four anchor screws. I taped the other ends of the test leads to the probes of a digital multimeter and set the dial to AC volts. Get an assistant to drive. See that you get a small voltage which should rise to approx 2 volts as the speed increases. When you have finished, remove the leads and re tighten the screws, firmly, but do not over torque them. Sorry, pictures won't load at the moment.

Happy to wang you some coin to fix this mate if I can't work it out myself which is very likely...lol

[mudnut]

No coin necessary, Andy. Anyway, I can't help, as I only have the one cluster, I am using to set up. The test procedure I laid out, should still work for your speedo. It confirms your sender and wiring harness are all good. If the signal is ok, then another unit from a wrecker or one of your minions from here may be the go. It is fairly easy to swap out the speedo so you can retain your odometer. Pop the black cluster shroud and clear cover off. Unplug the odometer connector. Undo the screws, ( also one near the high beam and indicators) and gently lift out the gauge. I could sling you a few bucks for postage, and your second cluster and stuffed speedo, so I can have go at dissecting it. It will also give me some spare gauges.